US Congress Returns to Final Stage of Iran Nuclear Deal Review

Congressional review of the international agreement on Iran's nuclear program enters its final stretch Tuesday, as U.S. lawmakers return from a month-long recess to consider measures officially disapproving the deal.

Congress has until September 17 to review the terms and vote for or against, and while the outcome appears increasingly certain, there is intrigue in how the process will play out over the course of the next week.

The biggest question involves the first step of whether the House and Senate, both controlled by Republicans, will pass a bill opposing the agreement. In the House, Republicans hold a large enough majority to easily get a disapproval measure through.

But things are more complicated in the Senate, where a slightly smaller Republican majority and quirkier rules mean Democrats have a chance of preventing a vote from even taking place. To do that, 41 senators would have to agree to not let the bill proceed to a vote. So far, 38 Senators, all Democrats and independents, have said they would vote against the bill, but that does not necessarily mean they would also help block a vote in the first place.

If both chambers approve the measure opposing the agreement, the next steps are more clear. President Barack Obama has promised to use his veto power to reject any opposition bill.

The U.S. system gives Congress one more chance in that situation, but overriding a presidential veto requires the high threshold of two-thirds support in both the House and Senate. That would mean 67 of the 100 Senators and 290 of the 435 House members opposing the Iran nuclear deal.

With 38 Senators already publicly declaring their support for agreement and several others yet to declare their position, President Obama has more than enough support to block the opposition bill and let the agreement go through.

Still, the debate will give critics further chance to voice their complaints about the agreement, which they see as too friendly to Iran by leaving too much of its nuclear program in place while unlocking billions of dollars that some fear will be used to support terrorism.